1. Field of the Invention
This invention relates in general to control of rod pumped wells and in particular to control of rod pumping equipment for conditions where heavy crude oil production creates viscous and rod drag forces that cause the rod string to fall slower than the pumping unit motion on the downstroke.
2. Description of the Prior Art
When heavy crude oil production creates viscous and rod drag forces that cause the rod string to fall slower than the pumping unit downstroke motion, the pumping unit equipment can be damaged resulting in excessive maintenance costs and reduced production. A prior solution to that problem has been to install a variable frequency drive on the pumping unit and to manually slow the motor speed so that the pump speed is slowed to minimize rod float induced events. The problem with this prior approach is that well conditions change. For example, where heavy crude oil is being produced, cyclic steam injection, steam assisted gravity drainage (SAGD) and other secondary recovery operations require that steam be injected in the well for a time period, followed by pumping the well for a period of time to recover water and heavy crude oil. Well head temperatures change with time, and ambient temperature conditions affect flowline pressures which can adversely affect the rod-pump system with respect to rod float, rod loading and other operational conditions.
3. Identification of Objects of the Invention
A primary object of the invention is to provide Rod Float Mitigation (RFM) methods to detect rod float during rod pumping operations and to control the rod pumping apparatus to mitigate damage to the equipment while maximizing production.